1. Field of the Invention
The present invention relates generally to the field of wireless communications and, more particularly, to wireless devices having self-locating capability.
2. Discussion of Related Art
Many radios have self localization capabilities, sometimes using global positioning satellite (GPS) systems. However, any radio may be denied access to GPS service due to the environment of usage at a give time. For example, radios used in densely built-up areas or in areas that are in the shadow of buildings, may be unable to receive a GPS signal due to blocking by the buildings or natural terrain.
Some radios also self-locate using radio frequency (RF) signaling to determine their range relative to other radios having known locations. This is done by measuring the time delay of a signal received by one radio from another radio at a known location. Methods of triangulation can be used to determine the location of the radio based on its range to at least three other radios with known locations. However, radios that use RF signaling to deduce range between one another may be susceptible to errors in the range calculation that arise when the radios are in a multi-path environment. Various processing techniques have been applied to the time delay calculation procedure in attempts to smooth motion of the radio through the occasional erroneous range calculation due to multi-path errors. These techniques include, for example, setting minimum thresholds for the received signal power, seeking the earliest arrival signal, and averaging or filtering sequential estimates.